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Appalachian State University: Business Letter Format
A site that lists the most important parts of a business letter. Very detailed. Also includes labeled samples of how an appropriate business letter should look.
Letter Writing Guide
How to Write an Apology Letter
This informational site for teachers and students explains the importance of a letter of apology. Then the article articulates the types of information to include in friendly/personal apology letters and in formal/business apology letters.